misc: mei: unregister misc device in pci_remove function

Since the misc device is registered only in the pci probe function
it has to be also unregistered in the counterpart pci remove function
and not in the module exit function.
In case of probe failure the driver was oopsing in module exit function.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>